Wood-type golf club head

ABSTRACT

A wood-type golf club head has a club face provided with a face roll, and the radius of curvature Y in inch of the face roll satisfies: Ma/Y=&lt;250 and Ma&gt;=3000, wherein Ma is a vertical moment of inertia in g sq·cm of the head around a horizontal axis extending through the center of gravity of the head in parallel with a toe-heel direction of the head.

BACKGROUND OF THE INVENTION

The present invention relates to a wood-type golf club head, moreparticularly to a club face having curvature specifically defined inrelation to a moment of inertia of the head in order to achieve carrydistance and steady directionality.

In the wood-type golf club heads, in order to increase the carrydistance, various studies have been made, and it has been known to beeffective to avoid so called “ballooning”, or “rising” trajectory byreducing the backspin of the golf ball at impact.

On the other hand, it is desirable that the carry distance is not sovaried even if the ball hitting positions of the club face are off thesweet spot upward or downward, therefore, it is desirable to decreasethe variation of backspin due to the change in the ball hitting positionin the up-and-down direction.

Such variation of backspin can be reduced by a face roll because theface roll can lessen the vertical gear effect.

As well known in the art, the vertical gear effect is as follows. If theball hitting position is off the sweet spot SS upwards or downwards,then as shown in FIG. 8, with respect to a horizontal axis extending inthe toe-heel direction passing through the center of gravity G of thehead, there is caused a moment which is a product of the impact force Freceived from the golf ball (b) and the distance L1 or L2 between thehitting position and the center of gravity G measured perpendicular tothe direction of the force F. As a result, the club head is rotatedaround the horizontal axis by a small angle.

Due to the frictional engagement between the golf ball and the club face(fn), the contact surface of the golf ball receives a force in thereverse direction to the rotational direction of the club head like agear. Accordingly, the backspin of the ball is decreased in the case ofan upper hitting position or increased in the case of a lower hittingposition.

By providing a face roll as shown in FIG. 9, the distance L1 or L2becomes relatively small, and the moment is decreased accordingly.Therefore, the vertical gear effect is lessened, and the variation ofbackspin is also decreased.

Further, in the case of the upper hitting position, the face roll canincrease the ball launch angle, therefore, a decrease in the ballisticheight due to the above-explained decrease in the backspin can becompensated thereby. On the other hand, in the case of the lower hittingposition, the face roll can decrease the ball launch angle, therefore,an increase in the ballistic height due to the above-explained increasein the backspin can be compensated thereby.

In recent years, on the other hand, large-sized wood-type golf clubheads are widely used. Such a large-sized head has a relatively largevertical moment of inertia Ma. As a result, even if the ball hittingpositions are off the sweet spot upward or downward, the above-mentionedrotation of the club head at impact becomes decreased, and the verticalgear effect is also lessened.

Therefore, in the case of the upper hitting position, the backspin isnot fully decreased due to the lessened vertical gear effect whereas thelaunch angle is increased by the face roll. As a result, the trajectoryis liable to become “rising” trajectory and thereby the carry distanceis decreased.

On the other hand, in the case of the lower hitting position, thebackspin is not fully increased due to the lessened vertical gear effectwhereas the launch angle is decreased by the face roll. As a result, theballistic height becomes very low, and again the carry distance isdecreased.

SUMMARY OF THE INVENTION

It is therefore, an object of the present invention to provide awood-type golf club head in which, although the vertical moment ofinertia is large, the decrease in the carry distance due to the ballhitting position which is off the sweet spot upward or downward, can belessened.

According to the present invention, a wood-type golf club head has aclub face provided with a face roll of which radius of curvature Y(inch) satisfies:

Ma/Y=<250 and

Ma>=3000

whereinMa is a vertical moment of inertia (g sq·cm) of the head around ahorizontal axis extending through the center of gravity of the head inparallel with a toe-heel direction of the head.

DEFINITIONS

In this specification, dimensions, positions, directions and the likerelating to the club head refer to those under a standard state of theclub head unless otherwise noted.

Here, the standard state of the club head is such that the club head isset on a horizontal plane HP so that the axis CL of the clubshaft (notshown) is inclined at the lie angle (alpha) while keeping the axis CL ona vertical plane VP, and the club face 2 forms its loft angle (beta)with respect to the horizontal plane HP. Incidentally, in the case ofthe club head alone, the center line of the shaft inserting hole 7 a canbe used instead of the axis CL of the clubshaft.

“Sweet spot SS” is the point of intersection between the club face 2 anda straight line N drawn normally to the club face 2 passing through thecenter of gravity G of the head.

“Back-and-forth direction” is a direction parallel with the straightline N projected on the horizontal plane HP.

“Heel-and-toe direction” is a direction parallel with the horizontalplane HP and perpendicular to the back-and-forth direction.

“up-and-down direction” is a direction perpendicular to the horizontalplane HP.

“Vertical moment of inertia Ma” is the moment of inertia of the headaround a horizontal axis passing through the center of gravity G inparallel to the toe-heel direction of the head.

“Lateral moment of inertia Mb” is the moment of inertia of the headaround a vertical axis passing through the center of gravity G.

“Face progression FP” is the horizontal distance of the leading edge Leof the club head 1 from the vertical plane VP including the club shaftcenter line CL, measured in a vertical plane including the sweet spot Ssand the center of gravity G as shown in FIG. 3.

“Edge” of the club face 2: if the edge (2 a, 2 b, 2 c and 2 d) isunclear due to smooth change in the curvature of the club face 2, avirtual edge line (Pe) which is defined based on the curvature change,is used instead as follows. As shown in FIGS. 6 and 7, in each cuttingplane E1, E2 . . . including the straight line N extending between thesweet spot SS and the center of gravity G, a point Pe at which theradius (r) of curvature of the profile line Lf of the face portion firstbecomes under 20 mm in the course from the center SS to the periphery ofthe club face is determined. Then, the virtual edge line is defined as alocus of the points Pe.

“wood-type golf club” is meant for at least number 1 to 5 woods, andclubs comprising heads having similar shapes may be included.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a wood-type golf club head according to thepresent invention.

FIG. 2 is a top view thereof.

FIG. 3 is a cross sectional view taken along line A-A in FIG. 2.

FIG. 4 is a cross sectional view of the face portion for explaining theface roll.

FIG. 5 is a cross sectional view of the face portion for explaining theface bulge.

FIGS. 6 and 7 are a front view and a cross sectional view of a faceportion for explaining the edge of the club face.

FIGS. 8 and 9 are cross sectional views for explaining a vertical geareffect.

FIGS. 10 and 11 are cross sectional views for explaining a horizontalgear effect.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the drawings, wood-type golf club head 1 according to the presentinvention comprises: a face portion 3 whose front face defines a clubface 2 for striking a ball; a crown portion 4 intersecting the club face2 at the upper edge 2 a thereof; a sole portion 5 intersecting the clubface 2 at the lower edge 2 b thereof; a side portion 6 between the crownportion 4 and sole portion 5 which extends from a toe-side edge 2 c to aheel-side edge 2 d of the club face 2 through a back face BF of the clubhead; and a hosel portion 7 at the heel side end of the crown to beattached to an end of a club shaft (not shown) inserted into the shaftinserting hole 7 a. Thus, the club head 1 is provided with a hollow (i)and a shell structure with the thin wall.

The club face 2 is provided with a face roll FR (a curvature from crownto sole) and a face bulge FB (a curvature from heel to toe). Further,the face 2 is provided with parallel score lines 9 extending straight inthe toe-heel direction. The score lines 9 are fine grooves for creatinga suitable friction between the face and ball at impact even in wetconditions so as to effectively prevent so called drop ball.

In order to reduce the weight of the head and to adjust the position ofthe center of gravity G of the head, fiber reinforced resins can be usedas light weight materials to form a part of the club head 1. But, inthis example, the club head 1 is made of one or more metal materialsonly. Various metal materials, for example, stainless alloys, maragingsteels, pure titanium, titanium alloys, magnesium alloys, aluminumalloys and the like can be used. But, the use of metal materials havinghigh specific tensile strength is desirable. In the case of titaniumalloys for example, Ti-6Al-4V, Ti-15V-3Cr-3Al-3Sn, Ti-15Mo-5Zr-3Al,Ti-13V-11Cr-3Al and the like can be suitably used.

The club head 1 can be manufactured by assembling two or more (usuallyup to 5 or 6) parts each prepared through a suitable process forexample, casting, forging, pressure molding or the like.

In this embodiment, the head is for a number 1 wood.

The volume of the club head 1 is preferably not less than 400 cc, morepreferably not less than 420 cc, still more preferably not less than 440cc in order to increase the moment of inertia and the depth of thecenter of gravity.

However, to prevent an excessive increase in the club head weight anddeteriorations of swing balance and durability, the club head volume ispreferably not more than 600 cc, more preferably not more than 500 cc.According to the golf rules, the club head volume is not more than 470cc, thus the volume is set to be 460 cc or less as circumstances demand.

The height h of the face 2 is set in a range of not less than 30 mm,preferably not less than 35 mm, more preferably not less than 40 mm, butnot more than 70 mm, preferably not more than 65 mm, more preferably notmore than 60 mm when measured between the upper edge 2 a and the loweredge 2 b in the vertical plane including the sweet spot as shown in FIG.4. If the height h is too small, it becomes difficult to hit the ball,and the impact resilience of the face is decreased to decrease the carrydistance. If the height h is too large, there is a possibility that theposition of the sweet spot SS becomes unfavorably high, and the carrydistance is decreased.

Also, the width FW of the face 2 is preferably set in a range of notless than 90 mm, more preferably not less than 95 mm, still morepreferably not less than 100 mm, but not more than 130 mm, morepreferably not more than 127 mm, still more preferably not more than 125mm when measured in the toe-heel direction between the toe-side edge 2 cand heel-side edge 2 d passing through the sweet spot SS as shown inFIG. 1.

The vertical moment of inertia Ma is set to be not less than 3000 (gsq·cm), preferably not less than 3200 (g sq·cm), more preferably notless than 3500 (g sq·cm), still more preferably not less than 3900 (gsq·cm).

Therefore, even if the ball hitting position is off the sweet spotupward or downward, the rotation of the club head 1 at impact around thehorizontal axis passing through the center of gravity can be reduced,and the vertical gear effect is lessened. Thereby, the variation ofbackspin due to the variation of the ball hitting positions is reduced.If the vertical moment of inertia Ma is less than 3000 (g sq·cm), itbecomes difficult to obtain these effects. If the vertical moment ofinertia Ma is too large contrary, there is possibility that the clubhead weight unavoidably increases or the shape of the club head becomespeculiar. Therefore, the vertical moment of inertia Ma is preferably notmore than 4500 (g sq·cm), more preferably not more than 4000 (g sq·cm).

Meanwhile, the ball launch angle becomes substantially equal to theangle of a normal line drawn to the club face 2 at the ball hittingposition. In the case that the radius of curvature Y of the face roll FRis small, if the ball hitting position is off the sweet spot SS upward,then the launch angle becomes relatively large, when compared with theball hitting position is the sweet spot SS. If the ball hitting positionis off the sweet spot SS downward, then the launch angle becomesrelatively small. In either event, the carry distance is decreased.

In the present invention, therefore, the radius of curvature Y (inch) ofthe face roll FR is limited in relation to the vertical moment ofinertia Ma (g sq·cm) as follows:

Ma/Y=<250

thereby, the increase in the launch angle at the time of upper hittingis reduced, and “ballooning” or “rising” trajectory can be prevented.Also, the decrease in the launch angle at the time of lower hitting isreduced, and the decrease in the carry distance due to the low ballisticheight can be prevented. Preferably, the ratio (Ma/Y) is not more than245, more preferably not more than 200, still more preferably not morethan 195. However, if the ratio (Ma/y) is less than 90, the ballisticcourse tends to become excessively low at the time of upper hitting, orexcessively high at the time of lower hitting, therefore, the ratio(Ma/Y) is not less than 90, preferably not less than 110, morepreferably not less than 130.

If the numerical value of the radius of curvature Y is less than 15inches, then the above-mentioned advantageous effects are lessened,therefore, the radius of curvature Y is preferably not less than 15inches, more preferably not less than 16 inches, still more preferablynot less than 20 inches.

Although the radius of curvature Y may be infinitely great, it ispreferred that the radius Y is not more than 100 inches, more preferablynot more than 50 inches, still more preferably not more than 40 inchesin order to slightly fix the ball launch angle at the upper and lowerhits because, even in the club head having a large vertical moment ofinertia Ma, slight vertical gear effect occurs.

In this embodiment, further, the lateral moment of inertia Mb is set ina range of not less than 4000 (g sq·cm), preferably not less than 4500(g sq·cm), more preferably not less than 5000 (g sq·cm), still morepreferably not less than 5200 (g sq·cm).

Therefore, even if the ball hitting position is off the sweet spottoward the toe or heel, the rotation of the head at impact around thevertical axis passing through the center of gravity G can be reduced. Asa result, by the user's intentional rotating of the head around theclubshaft center line CL to the proper address position, thedeterioration of directionality of the struck ball can be avoided.

But, if the lateral moment of inertia Mb is too large, then there ispossibility that the club head weight unavoidably increases or the shapeof the club head becomes peculiar. Therefore, the lateral moment ofinertia Mb is preferably not more than 8000 (g sq·cm), more preferablynot more than 6000 (g sq·cm).

When the lateral moment of inertia Mb has a relatively large value asabove, similar phenomenon to that explained in relation to the verticalgear effect occurs as follows.

In the case that the ball hitting position is off the sweet spot SStowards the toe, as shown in FIG. 10 (illustrating a right-handed case),the club head 1 is rotated clockwise around the center of gravity G, anda counterclockwise sidespin is given to the ball (b). On the other hand,in the case that the ball hitting position is off the sweet spot SStowards the heel, the club head 1 is rotated counterclockwise around thecenter of gravity G, and a clockwise sidespin is given to the ball (b).Such phenomenon is known as horizontal gear effect.

Due to the sidespin, therefore, the struck ball is liable to travel outof the target trajectory J to the left or right.

Such deviation, namely, deterioration of the directionality due to thehorizontal gear effect can be reduced by a face bulge.

By providing a face bulge, as shown in FIG. 11, in the case that theball hitting position is off the sweet spot SS toward the toe (toe-sidehitting), the ball is launched rightward at an angle θt with respect tothe target trajectory j, and due to the sidespin (hook spin), the ballreturns towards the target trajectory j. In the case that the ballhitting position is off the sweet spot SS toward the heel (heel-sidehitting), the ball is launched leftward at an angle θh with respect tothe target trajectory j, and due to the sidespin (slice spin), the ballreturns towards the target trajectory j. Thus, the deterioration of thedirectionality is reduced.

When the lateral moment of inertia Mb becomes more than 4000 (g sq·cm),the horizontal gear effect is decreased, and accordingly the sidespin isdecreased whereas the ball is launched at the angle θt or θh due to theface bulge at the time of toe-side or heel-side hitting. Accordingly,there is possibility that the face bulge deteriorates thedirectionality.

In this embodiment, therefore, the face bulge FB is provided with aradius of curvature X (inch) satisfying

Mb/X=<350

whereinMb is the above-mentioned lateral moment of inertia in g sq·cm.Preferably, the ratio (Mb/x) is not more than 325, more preferably notmore than 260, but not less than 50, more preferably not less than 100,still more preferably not less than 130.As a result, the horizontal launch angle θt or θh at the time oftoe-side or heel-side hitting, is optimized and the deterioration of thedirectionality can be prevented. If the ratio (Mb/X) is less than 350,hook tendency and slice tendency become noticeable at the time oftoe-side hitting and heel-side hitting, respectively.

The numerical value of the radius of curvature X of the face bulge FB ispreferably not less than 15 inches, more preferably not less than 16inches, still more preferably not less than 20 inches. If the radius Xis less than 15 inches, the above-mentioned advantageous effect tends todecrease. Although the radius of curvature X may be infinitely great, itis preferred that the radius X is not more than 100 inches, morepreferably not more than 50 inches, still more preferably not more than40 inches, so that the ball is launched at a small horizontal launchangle at the time of toe-side or heel-side hitting because, even in theclub head having a large lateral moment of inertia Mb, slight horizontalgear effect occurs.

In this embodiment, the vertical moment of inertia Ma is less than thelateral moment of inertia Mb. In this case, there is a tendency that thevertical gear effect comes out stronger than the horizontal gear effect.Therefore, it is desirable to make the radius of curvature Y of theface-roll FR less than the radius of curvature X of the face bulge FB inorder to lessen the difference between the vertical and horizontal geareffects. Preferably, the radius ratio (X/Y) is not less than 1.2, morepreferably not less than 1.5. But, if the ratio (X/Y) is more than 3.5,the radius of curvature Y of the face roll is decreased and theabove-mentioned negative aspects arise, therefore, the radius ratio(X/Y) is not more than 3.5, more preferably not more than 3.0.

In this embodiment, the face roll FR and face bulge FB extend over thealmost entirety of the club face 2.

The center of the radius of curvature Y is positioned backwardly farfrom the center of gravity G.The center of the radius of curvature X is positioned backwardly farfrom the center of gravity G of the head.In the vertical plane including the sweet spot SS and the center ofgravity G, as shown in FIG. 4, at least between an upper point Pu 10 mmdownward from the upper edge 2 a of the face 2 and a lower point Pd 10mm upward from the lower edge 2 b of the face 2, the radius of curvatureY is a single radius.In the horizontal plane including the sweet spot SS, as shown in FIG. 5,at least between a toe-side point Pt 20 mm toward the sweet spot fromthe toe-side edge 2 c and a heel-side point Ph 20 mm toward the sweetspot from the heel-side edge 2 d, the radius of curvature X is a singleradius.However, in the above-mentioned range between (Pu and Pd) or (Pt andPh), the radius Y or X may be varied as far as the above-mentionedlimitations are satisfied.

In this embodiment, further, the face progression FP is increased to atleast 20 mm, preferably not less than 21 mm as shown in FIG. 3. Byincreasing the face progression FP in this way, the center line CL ofthe shaft axis is relatively shifted toward the backward of the clubface. Namely, without decreasing the lateral moment of inertia Mb andthe depth GL2 of the center of gravity G, the center line CL of theshaft axis approaches the center of gravity G, and the moment of inertiaMc of the head around the center line CL is decreased.

Therefore, it becomes easy even for the beginner and intermediategolfers to rotate the head around the clubshaft center line CL duringswing. As the club head 1 is easy to control, in cooperation with thelarge lateral moment of inertia Mb, good directionality can be obtained.But, if the face progression FP is excessively large, then the moment ofinertia Mc decreases and the club head is liable to rotate in excess. Asa result, hook tends to occur. Further, it becomes difficult to addressthe ball. In this light, the face progression FP is preferably not morethan 25 mm, more preferably not more than 24 mm, still more preferablynot more than 23 mm.

Comparison Tests

Wood-type hollow metal heads were prepared and tested for carry distanceand directionality.

Each of the club heads was composed of:

a hollow main body formed by casting a titanium alloy Ti-6Al-4V andprovided with an opening in the crown portion;a tungsten-alloy weight fixed to the inside of the main body by the useof an epoxide resin adhesive; anda crown plate formed by forging a titanium alloy Ti-15V-3Cr-3Sn andfixed to main body by laser-welding so as to cover the opening.The specifications common to all of the heads are as follows:

Head volume: 460 cc

Head mass: 198 g

Lie angle: 58 degrees

Loft angle: 10.5 degrees

Face height h: 52 mm

Face width FW: 105 mm

Thickness of the crown portion: 0.4 mm

Thickness of the face portion:

-   -   3.8 mm in a central portion including the sweet spot    -   2.5 mm in the peripheral portion        The moments of inertia Ma and Mb were changed by changing the        thicknesses of the sole portion, side portion and/or crown        portion, the mass of the weight member, the position of the        hosel portion as shown in Tables 1, 2 and 3.

Carry Distance Test:

Each of the club heads was attached to a FRP shaft (“MP400” manufacturedby SRI Sports Limited, flex R, mass 48 grams) to make a number 1 wood,and the wood club was mounted on a swing robot. Then, the each head hitthree-piece balls (SRIXON Z-UR, manufactured by SRI Sports Limited) sixtimes par each of the following five hitting positions to obtain theaverage carry distance of the six shots. The head speed was 45meter/second.

Hitting Positions:

Center: sweet spot SS

Upside: 10 mm upside of SS

Downside: 10 mm downside of SS

Toe-side: 10 mm toe-side of SS

Heel-side: 10 mm heel-side of SS

Directionality Test (Deviation from Target Trajectory)

Five golfers having handicap ranging from 10 to 20 hit theabove-mentioned three-piece balls ten times each with each of theabove-mentioned golf clubs.

The deviation or difference of the stop position of the struck ball fromthe target trajectory was measured in each shot, and “+” plus sign and“−” minus sign which mean slice and hook, respectively, were added tothe measurements. Using such measurements, the following criteria werecalculated:Average deviation (average of 50 shots=10 shots×5 golfers);Slice tendency (average of most sliced five shots of 5 golfers);Hook tendency (average of most hooked five shots of 5 golfers);Maximum variation (slice tendency−hook tendency).The test results are shown in Tables 1 to 3.

TABLE 1 Ref. 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ref. 2 Ex. 6 Ref. 3 Ex. 7Head Vertical moment Ma (g sq.cm) 3900 3900 3900 3900 3900 3900 32003200 4500 4500 Lateral moment Mb (g sq.cm) 5200 5200 5200 5200 5200 52004500 4500 6000 6000 Face progression FP (mm) 22 22 22 22 22 22 22 22 2222 Face bulge radius X (inch) 30 30 30 30 30 30 30 30 30 30 Face rollradius Y (inch) 12 16 20 25 30 40 12 20 12 30 Ma/Y 325 244 195 156 13098 267 160 375 150 Mb/X 173 173 173 173 173 173 150 150 200 200 X/Y 2.51.9 1.5 1.2 1.0 0.8 2.5 1.5 2.5 1.0 Carry distance (m) Center 254 253253 254 255 254 252 253 256 255 Upside 241 244 246 249 246 243 240 246240 248 Downside 232 235 238 243 240 234 230 238 230 240 Toe-side 245246 245 246 245 245 241 241 246 247 Heel-side 234 235 235 234 234 235232 233 236 237

TABLE 2 Ex. 2 Ex. 8 Ex. 9 Ex. 10 Head Vertical moment Ma (g sq.cm) 39003900 3900 3900 Lateral moment Mb (g sq.cm) 5200 5200 5200 5200 Faceprogression FP (mm) 22 18 20 24 Face bulge radius X (inch) 30 30 30 30Face roll radius Y (inch) 20 20 20 20 Ma/Y 195 195 195 195 Mb/X 173 173173 173 X/Y 1.5 1.5 1.5 1.5 Carry distance (m) Center 253 252 253 252Upside 246 246 246 247 Downside 238 237 238 237 Toe-side 245 242 243 244Heel-side 235 236 235 235 Directionality Average deviation (m) −1 10 4−9 Slice tendency (m) 9 22 14 0 Hook tendency (m) −8 0 −5 −18 Maximumvariation (m) 17 22 19 18

TABLE 3 Ex. 2 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 15 Head Vertical moment Ma(g sq.cm) 3900 3900 3900 3900 3900 3900 Lateral moment Mb (g sq.cm) 52005200 5200 5200 5200 5200 Face progression FP(mm) 22 22 22 22 22 22 Facebulge radius X (inch) 30 12 16 20 40 50 Face roll radius Y (inch) 20 2020 20 20 20 Ma/Y 195 195 195 195 195 195 Mb/X 173 433 325 260 130 104X/Y 1.5 0.6 0.8 1.0 2.0 2.5 Carry distance (m) Center 253 250 251 251252 251 Upside 246 245 246 246 247 245 Downside 238 239 239 238 238 239Toe-side 245 239 241 243 244 242 Heel-side 235 230 231 232 233 231Directionality Average deviation (m) −1 4 2 1 2 2 Slice tendency (m) 918 15 13 12 16 Hook tendency (m) −8 −14 −12 −9 −8 −12 Maximum variation(m) 17 32 27 22 20 28

1. A wood-type golf club head having a club face provided with a faceroll whose radius of curvature Y in inch satisfies:Ma/Y=<250 andMa>=3000, wherein Ma is a vertical moment of inertia in g sq·cm of thehead around a horizontal axis extending through the center of gravity ofthe head in parallel with a toe-heel direction of the head.
 2. The golfclub head according to claim 1, wherein a lateral moment of inertia Mbof the head around a vertical axis extending through the center ofgravity of the head is not less than 4000 g sq·cm.
 3. The golf club headaccording to claim 2, wherein the club face has a face progression ofnot less than 20 mm.
 4. The golf club head according to claim 3, whereinthe club face is provided with a face-bulge whose radius of curvature Xin inch satisfies:Mb/x=<350 wherein Mb is said lateral moment of inertia in g sq·cm. 5.The golf club head according to claim 2, wherein the club face isprovided with a face bulge whose radius of curvature X in inchsatisfies:Mb/x=<350 wherein Mb is the lateral moment of inertia in g sq·cm.
 6. Thegolf club head according to claim 5, wherein the vertical moment ofinertia Ma is less than the lateral moment of inertia Mb.
 7. The golfclub head according to claim 6, wherein the radius ratio (X/Y) is notless than 1.2.
 8. The golf club head according to claim 5, wherein theradius ratio (X/Y) is not less than 1.2.